Type in that address, (Assuming that IS the address of your Linksys router) in a browser address bar.

It will then prompt for a user ID and password, enter then.
And you're in.

If you've forgotten your UserUD/password, you can reset the modem via some little button somewhere on the router (read your manual), then the password is reset to blank probably, you'll need to read your manual for how it is reset.
Note if you DO reset your router, all the settings will be lost.